Eco & Evo: Nutrient Cycling

Phosphorus cycle

Most P is physically inaccessible (marine sediments, deep ocean, mineral deposits), major sources - weathering of rocks, volcanoes, usually slow trickle - needed in nucleic acids, organisms recycle in efficiently

Carbon cycle

Photosynthesis and cellular respiration cycle C between pools, producers sequester CO₂ from air as sugar, consumers and deforestation releases stored C back to the atmosphere

How humans affect the carbon cycle

Burning fossil fuels, habitat degradation, deforestation = decrease primary producers and leaves dead things to decompose, release carbon dioxides, forest fires

Human effect on carbon cycles affect corals

Temp → increase coral bleaching, CO₂ → decrease pH in water

Greenhouse effect

CO₂ is a greenhouse gas → increases Earth’s temperature, leads to coral reef loss

Biological N fixation

Putting N into a usable form, converts N₂ → NH₃, requires immense amount of energy

Nitrification

converts NH₃ → NO₂ → NO₃, Nitrosifying bacteria convert NH₃ → NO₂, Nitrifying bacteria convert NO₂ → NO₃

Decomposers/detritovores

Give it back to the soil through ammonification (N) or mineralization (all nutrients)

Dentrification

Converts NO₂ and NO₃ → N₂, anaerobic process, carried out by anaerobic bacteria

How nitrogen returns to atmosphere

Anammox - NH₃ + NO₂ → N₂H₄ (hydrazine) → N₂ + H₂O

Global nitrogen cycle

In terrestrial systems N fixation and nitrification are much greater than denitrification because of industrial processes, agriculture, and livestock - most N cycling occurs in oceans

Mineralization

Breakdown of organic molecules into inorganic molecules

Immobilization

Occurs when organisms convert inorganic molecules into organic molecules

Rivers nutrient overload

Rivers decrease immobilization and denitrification rates with increasing N loads, dead zones

Forests affect on river nitrogen

Loss of trees around rivers increase nutrients and nitrogen into rivers because trees can no longer take up these resources

Biotic processes contribute to nutrient cycles

Fungi can improve nutrient retention under low nutrient conditions, grazing by large herbivores increase rate of nutrient cycling, predators by removing herbivores or altering their diet